The present invention is directed to an analog clock driven by radio signals with automatic resetting means.
An analog clock is by definition one which uses a dial face with hour and minute markings and a set of hands to indicate the hour and minute and second. Such timepieces are constructed using a chain of wheels with a proper gear ratio such that as a seconds wheel rotates it progressively turns the minutes wheel and then the hour wheel and thus rotates the hands which are fixed to the shafts of the wheels. The seconds wheel is typically coupled to a stepper motor that is controlled by an associated integrated circuit. Electrical pulses are input to the stepper motor causing the seconds wheel to turn in synchronization with the incoming pulses. In the United States, a radio station WWVB sends a time-coded signal which can be used to control either analog clocks or digital clocks so that the time is always in synchronization with the actual broadcast radio time. Such signal includes the change to and from Daylight Savings Time to automatically reset a clock receiving such signal.
If a clock temporarily malfunctions or its power source is removed, then of course, the clock must be reset. With a digital clock and display this can be done electronically. However, with an analog clock without modification, the driving circuit cannot know what is the erroneous setting of the analog clock display in order to correct it. Prior techniques have used feedback systems incorporating either magnetic or optical means to sense the actual positions of the hands of the analog clock. This is expensive and may not always function adequately.
If the user of the clock is required to reset the time, it is time consuming and in any case, the time accurate to the nearest second is not achievable.
Specifically, one technique of resetting analog hands is using a setting wheel incorporated in the wheel chain so that it is locked into the minutes wheel during setting. A knob fixed to the shaft of the setting wheel for rotation by a user. The minute wheel also rotates the hour wheel at {fraction (1/60)}th of its own speed, and thus the time can be set. This setting method is cumbersome involving too many rotations. Also, since only the minute wheel is set, seconds cannot be set successfully.
Another method is to reset the analog clock electronically by the use of a setting button. Pressing of the button causes the stepper motor to automatically rotate the minute wheel at a relatively fast speed. The user stops at the appropriate time. Again the seconds cannot be adequately set and since only the minutes wheel is actuated, a long time as much as 60 seconds may be required to set the hour hand across a 12-hour span.
All of the foregoing defeats the purpose of an automatically radio controlled clock.
It is a general object of the present invention to provide an analog clock driven by radio signals with automatic resetting means.
In accordance with the above object, in a clock display driven by a radio signal providing an actual radio time, such display has an analog clock and display driven by the radio signal and a contiguous digital clock and display. A method of automatically resetting to the actual radio time the analog clock displays without use of feedback, either electrical or mechanical, from the analog display comprising the steps of stopping the analog and digital display and providing user manual controls which allow the user to set the digital display time to the displayed analog time which has been stopped. Thereafter the digital display is compared to the actual radio time and, if less, the analog clock is run at a fast rate until the displayed time is equal to the actual radio time; if more, the analog clock is run at a slow rate until equal. When equal, the analog clock is run responsive to the radio time.